Natural cellulosic feedstocks typically are referred to as “biomass”. Many types of biomass, including wood, paper, agricultural residues, herbaceous crops, and municipal and industrial solid wastes derived from crops have been considered as feedstocks for the manufacture of a wide range of goods. These biomass materials consist primarily of cellulose, hemicellulose, and lignin bound together in a complex gel structure along with small quantities of extractives, pectins, proteins, and ash. Due to the complex chemical structure of the biomass material, microorganisms and enzymes cannot effectively attack the cellulose without prior treatment because the cellulose is highly inaccessible to enzymes or bacteria. This inaccessibility is illustrated by the inability of cattle to digest wood with its high lignin content even though they can digest cellulose from such material as grass. Successful commercial use of biomass as a chemical feedstock depends on the separation of cellulose from other constituents.
The possibility of producing sugar and other products from cellulose has received much attention. This attention is due to the availability of large amounts of cellulosic feedstock, the need to minimize burning or landfilling of waste cellulosic materials, and the usefulness of sugar and cellulose as raw materials substituting for oil-based products. Other biomass constituents also have potential market values.
The separation of cellulose from other biomass constituents is difficult, in part because the chemical structure of lignocellulosic biomass is so complex. See, e.g., ACS Symposium Series 397, “Lignin Properties and Materials”, edited by G. W. Glasser and S. Sarkanen, published by the American Chemical Society, 1989, which includes the statement that “[L]ignin in the true middle lamella of wood is a random, three-dimensional network polymer comprised of phenylpropane monomers linked together in different ways. Lignin in the secondary wall is a nonrandom two-dimensional network polymer. The chemical structure of the monomers and linkages which constitute these networks differ in different morphological regions (middle lamella vs secondary wall) different types of cell (vessels vs fibers) and different types of wood (softwoods vs hardwoods). When wood is delignified, the properties of the macromolecules made soluble reflect the properties of the network from which they are derived.” The separation of cellulose from other biomass constituents is further complicated by the fact that lignin is intertwined and linked in various ways with cellulose and hemicellulose both of which are polymers of sugars. Thus there is a need for systems and methods for separating solid biomass (such as lignocellulosic biomass) into its constituent components and treating the components to make useful products. These and other needs are addressed by the present invention.